1. Field of the Invention
This invention is directed to polymer compositions and a method. More specifically, this invention concerns itself with the alleviation of problems associated with the preparation of blends from two or more essentially incompatible polymeric materials, such as relatively inflexible polyvinyl chloride or chlorinated polyvinyl chloride and ethylene-propylene (EPM) elastomers or ethylene-propylene-diene (EPDM) elastomers.
2. Description of the Prior Art
The prior art is replete with references which describe various means and methods for enhancement of the impact resistance of relatively rigid thermoplastics such as polyvinyl chloride (hereinafter PVC) and chlorinated polyvinyl chloride (hereinafter CPVC)--see for example U.S. Pat. No. 3,299,182 which discloses blends of CPVC and chlorinated polyethylene. Acrylonitrile/butadiene/styrene (ABS) compositions can also be modified in a similar fashion, see for example, U.S. Pat. No. 3,887,648. As disclosed in the above patents, these relatively rigid polymers can be compounded with one or more elastomers or mixtures of elastomers or other functionally similar material, each of which being tailored to impart improved processing and/or improved end-use characteristics of the rigid polymer. Typically, these elastomers contain a pendant group or a segment within their backbone which is common to or has improved compatibility with the rigid polymer (see, for example, U.S. Pat. Nos. 4,021,508; 3,994,995; 3,906,059; 3,891,725; and 4,035,440). The relatively rigid polymer can be combined with the elastomeric materials by dry blending (U.S. Pat. No. 3,994,995) or by the in situ polymerization of a vinyl monomer in the presence of an EPDM type elastomer, (U.S. Pat. No. 3,906,059).
Two component thermoplastic blends of certain EPM or EPDM elastomers with other thermoplastic olefins are known to form homogeneous easily moldable compositions which can be formed into tough flexible articles (see U.S. Pat. Nos. 3,919,358 and 4,036,912). Ordinarily, such blends lack intrinsic flame resistant properties, exhibit poor adhesion to polar substrates and cannot be dielectrically sealed. It is hypothesized that many of these deficiencies could be overcome if certain EPM or EPDM elastomers were to be blended with chlorine containing thermoplastic, such as PVC or CPVC. Prior attempts at combining such materials have proven largely unsuccessful due to the relative incompatibility between such materials. Such incompatibility can reportedly be overcome where the PVC is chemically engrafted upon the elastomer. This grafting process is economically unattractive.
Certain chlorinated polyethylene (CPE) elastomers have been found to be suitable for enhancement in the impact resistance of PVC and CPVC for some specific applications, (see for example U.S. Pat. Nos. 3,994,995 and 3,856,891). The chlorinated polyethylenes are not, however, acceptable substitutes for the EPM and EPDM type elastomers in PVC and CPVC. The reason for this lack of equivalency is quite simple, namely, the glass transition temperature (T.sub.g) of chlorinated polyethylene is about 5.degree. F.; whereas, the glass transition temperature (T.sub.g) of EPM and EPDM elastomers is about -60.degree. F. It is thus readily apparent that the EPM and EPDM elastomers are superior for enhancing the impact resistance of thermoplastics such as PVC and CPVC over a broader temperature range since the thermoplastics which are compounded with EPM and EPDM elastomers retain their impact resistance at much lower temperatures.
It would thus appear from the above discussion, that there is a continuing need for enhancement in the impact resistance of thermoplastic materials such as PVC and CPVC over broad temperature ranges and that the blends which are currently available do not retain such impact resistance at depressed temperatures.